This invention relates to molding footwear lasts.
Over the years the wood last has for the most part been replaced by lasts made of high density polyethylene. Typically, high density polyethylene lasts are fabricated by extruding and annealing a polyethylene club, and then carrying out a multi-step machining process to match a wood model. It may be necessary to produce replicate lasts (e.g., anywhere from two to 1,000 or more) corresponding to each of a number of differently sized last models for a production run of a given shoe design. Since many of the individual lasts are often used for very short production runs, the desirability of a low cost last has long been apparent.
Accordingly, many efforts have been made over the years to produce a low cost, high quality, molded plastic last. These efforts have as yet not yielded commercially acceptable results, in part because of high mold costs (particularly when only a few lasts are to be made from a given mold), in part because of the difficulty in finding a material that has the mechanical characteristics needed in a last and is at the same time capable of being molded in thick and irregular sections in economical cycle times.
Further background appears in U.S. Pat. Nos. 2,247,818; 2,521,072; 2,602,193; 2,617,129; 2,678,293; 2,850,752; 3,067,442; and 3,181,186.
Practice of the invention requires use of so-called instant set polymer, a class of material disclosed and claimed in U.S. Pat. No. 3,726,827 (the text of which is hereby incorporated by reference), said class as claimed in said patent being referred to hereinafter as ISP. The chemical structure and methods of making ISP form no part of the present invention. A species (hereinafter referred to as commercial ISP) of instant set polymer is commercially available from The Dow Chemical Company under the trade designation ISP.